1. Field of the Invention
Generally, the present invention relates to an optical radiation sensor system.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of microwatt seconds per square centimetre). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UV Max, Trojan UV Swift and UV8000, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation.
Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the trade-names UV3000 and UV4000, employ the same principal to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:
U.S. Pat. No. 4,482,809 [Maarschalkerweerd],
U.S. Pat. No. 4,872,980 [Maarschalkerweerd],
U.S. Pat. No. 5,006,244 [Maarschalkerweerd],
U.S. Pat. No. 5,418,370 [Maarschalkerweerd],
U.S. Pat. No. 5,539,210 [Maarschalkerweerd],
U.S. Pat. No. 5,590,390 (Re. 36,896) [Maarschalkerweerd],
U.S. Pat. No. 7,045,102 [Fraser et al.], and
U.S. patent application Ser. No. 11/078,706 [From et al.].
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water under treatment. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection process. The information so-obtained may be used to control lamp output to a desired level.
It is known in the art to monitor the ultraviolet radiation level by deploying one or more sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These sensor devices may be photodiodes, photoresistors or other devices that respond to the impingement of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (e.g., in volts or amperes) on output leads.
In most commercial ultraviolet water disinfection systems, the single largest operating cost relates to the cost of electricity to power the ultraviolet radiation lamps. In a case where the transmittance of the fluid varies from time to time, it would be very desirable to have a convenient means by which fluid transmittance could be measured for the fluid being treated by the system (or the fluid being otherwise investigated) at a given time. Indeed, the measurement of fluid transmittance is a requirement of the United States E.P.A. for municipal drinking water systems. If it is found that fluid transmittance is relatively high, it might be possible to reduce power consumption in the lamps by reducing the output thereof. In this way, the significant savings in power costs would be possible.
The measurement of fluid transmittance is desirable since measurement of intensity alone is not sufficient to characterize the entire radiation field—i.e., it is not possible to separate the linear effects of lamp aging and fouling from exponential effects of transmittance. Further, dose delivery is a function of the entire radiation field, since not all fluid takes the same path.
First generation optical radiation sensors, by design or orientation, normally sense the output of only one lamp, typically one lamp which is adjacent to the sensor. If it is desirable to sense the radiation output of a number of lamps, it is possible to use an optical radiation sensor for each lamp. A problem with this approach is that the use of multiple sensors introduces uncertainties since there can be no assurance that the sensors are identical. Specifically, vagaries in sensor materials can lead to vagaries in the signals which are sent by the sensors leading to a potential for false information being conveyed to the user of the system.
Another problem with such first generation optical radiation sensors is that it is not possible to ascertain the lamp output of a single lamp in an array of lamps which operate within the field of view of a single sensor.
A further problem with such first generation sensors is that, if the U.V. transmittance of the fluid being treated was unknown, two sensors would be required to determine the dose delivered to the fluid—i.e., one sensor to measure lamp intensity and one sensor to measure U.V. transmittance.
This lead to the development of second generation sensors such as the sensor described in U.S. Pat. No. 6,512,234 [Sasges et al. (Sasges)]. The Sasges optical radiation sensor device includes a radiation collector for receiving radiation from a predefined arc around the collector within the field and redirecting the received radiation along a predefined pathway; motive means to move the radiation collector from a first position in which a first portion of the predefined arc is received by the radiation collector and a second position in which a second portion of the predefined arc is received by the radiation collector; and a sensor element capable of detecting and responding to incident radiation along the pathway when the radiation collector is in the first position and in the second position.
The Sasges optical radiation sensor represents an important advance in the art in that it provides for an optical radiation sensor system which allows determination of lamp output information for a single lamp in an array of lamps. An additional advantage of the Sasges optical radiation sensor device is that a single sensor device can be used to determine the dose delivered to the fluid (i.e., in place of the multiple sensors conventionally required using first generation sensors). Thus, the provision of the Sasges optical radiation sensor device allows for on-line determination of U.V. transmittance (also known in the art as “UVT”) of the fluid being treated in an ultraviolet radiation lamp array.
Another second generation sensor device is described in U.S. Pat. No. 6,818,900 [Ellis et al. (Ellis)]. In its preferred form, the Ellis sensor device altered fluid layer thickness between a radiation source and a radiation sensor by: (i) moving the radiation source while keeping the radiation sensor stationary; (ii) moving the radiation sensor while keep the radiation source stationary; or (iii) moving a boundary element interposed between a stationary radiation source and a stationary radiation sensor.
Thus, Ellis sensor device requires a single lamp and single sensor element. The sensor element and radiation source are arranged to create a fluid layer therebetween. By altering the thickness of the fluid layer, it is possible to take multiple (i.e., two or more) radiation intensity readings at multiple, known fluid layer thicknesses. Once these are achieved, using conventional calculations, it is possible to readily calculate the radiation transmittance of the fluid.
Despite the developments made to date in first and second generation sensors, there is room for improvement. Specifically, it would be desirable to have an optical radiation sensor system having one or more of the following features:                a modular design making the sensor system appropriate for use with one or more of various radiation sources, fluid thickness layers and/or UVT conditions;        built-in diagnostics for parameters such as sensor operation, radiation source output, fluid (e.g., water) UVT, radiation source fouling (e.g., fouling of the protective sleeve surrounding the radiation source) and the like;        incorporation of an integrated reference sensor;        relatively safe and ready reference sensor testing;        UVT measurement capability; and/or        relatively low cost and ease of manufacture.        